JPH04318036A - Method for washing - Google Patents

Abstract

PURPOSE:To wash a substrate (a polymeric substance or a mold for molding the polymeric substance) to which a monomer, an oligomer or a polymer sticks at a low cost without causing environmental problems, danger to human bodies, deterioration in quality of the substrate, etc. CONSTITUTION:A substrate (a polymeric substance or a mold for molding the polymeric substance) to which a monomer, an oligomer or a polymer sticks is washed with (A) an aqueous solution using a shower. (B) The washed substrate is subsequently dipped in a solution containing a surfactant (preferably a nonionic surfactant). (C) The resultant substrate is then subjected to ultrasonic cleaning by using a surfactant-containing aqueous solution in which the dissolved gas concentration is kept at a prescribed value or above (the dissolved oxygen concentration is >=7ppm at ordinary temperature when the dissolved gas is air) by a method for forcibly feeding a gas with a peripheral pump. (D) Dipping, ultrasonic cleaning or dip jet washing is subsequently carried out by using a solution containing an organic solvent (preferably N-methyl-2-pyrrolidone) freely miscible with water. (E) The obtained substrate is then dried by centrifuging or with hot air and pure water blowing up to carry out washing of the substrate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning electronic parts, optical parts, mechanical parts, etc.

0002

[Prior Art] Conventionally, methods for cleaning substrates include using Freon 113, trichlorethylene (hereinafter referred to as Trichloroethylene),
Ultrasonic cleaning using trichloroethane (triethane) or methylene chloride (methylene chloride) is used.

Since Freon 113 is an ozone layer depleting substance, there is an urgent need for a substitute for it. Furthermore, trichlene, triethane, or methoxychloride are highly likely to be carcinogenic substances, and are extremely dangerous if they leak, so there are calls for their use to be reduced or prohibited. Although many alternative cleaning agents have been developed, they have many problems such as high cost and inability to ensure satisfactory cleaning performance compared to the above-mentioned solvents, and it is not easy to replace the above-mentioned solvents.

0004

The conventional techniques have problems such as environmental destruction, danger to the human body, increased cost, and decreased cleaning quality.

[0005]The present invention is intended to solve these problems, and its purpose is to provide a cleaning method that achieves high cleaning quality at a low cost using a cleaning agent that does not cause environmental damage or danger to the human body. It is to provide.

[0006]

[Means for Solving the Problems] The present invention includes a step of performing shower cleaning using at least an aqueous solution in cleaning a substrate to which at least one of monomers, oligomers, or polymers is attached, and then a step of performing shower cleaning using at least an aqueous solution; A process of immersion/ultrasonic cleaning using an aqueous solution in which the dissolved gas concentration is maintained at least above a certain value, followed by immersion/ultrasonic cleaning using a solution containing at least an organic solvent that freely mixes with water. It is characterized by having a step of performing immersion/jet cleaning, and further a step of drying by centrifugation, hot air, or pulling up pure water.

[0007] Regarding the shower cleaning process, this process is a process for more simply removing dirt with relatively low adhesion adhering to the substrate.

Regarding the surfactant, any of cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants can be used, but particularly good results have been obtained with nonionic surfactants. show.

[0009] It is necessary to use a highly concentrated solution for immersion, but a very dilute concentration can be used for ultrasonic cleaning. It is desirable that the solution temperature be as high as possible, but for nonionic surfactants, it is most desirable that it be just below the cloud point, and for other solutions, it is also desirable that it be 80 degrees Celsius or lower from the viewpoint of damage to the substrate to be cleaned and work environment problems.

[0010] Methods for keeping the dissolved gas concentration above a certain value include a method of directly feeding gas into the liquid, a method of using a semipermeable membrane, and a method of forcibly feeding gas with a vortex pump. In particular, the method using a vortex pump is excellent in terms of the structure of the washer. The dissolved gas concentration must be at least such that fine bubbles can be seen when ultrasonic waves are applied. For example, when air is dissolved in water at room temperature, the dissolved oxygen concentration must be 7 ppm or more.

[0011] Regarding ultrasonic waves, there are various selection ranges depending on the type of dirt and the type of substrate.
A frequency of 40 kHz is good, and a higher frequency of 100 kHz or more is considered to be effective for fine dirt of several tens of microns or less.

[0012] Organic solvents that mix freely with water include lower alcohols, ketones, cellosolves, and glycols, but N-methyl-2-pyrrolidone has particularly high dissolving power and can remove stains that cannot be removed in the previous process. It is effective as a final cleaning because it dissolves and removes even if it is present. Organic solvents that do not mix freely with water have many problems, such as not being able to use water in the subsequent rinsing step, and are not very preferred, but they can be used if they can be easily dispersed in water using a surfactant.

[0013] In the drying process, a pure water pulling drying method is preferable in the case of a substrate that has a smooth shape and is particularly easy to break, and a centrifugal separation drying method is preferable for a substrate that is small and difficult to break even if it has a smooth shape. A conventional drying method using hot air can also be used. Steam drying using Freon 113, isopropyl alcohol, etc. can also be used, but this is not very preferable because it has many problems such as environmental problems and safety.

[0014]

[Operation] According to the present invention, shower cleaning is performed first;
This step is a step for more simply removing dirt with relatively low adhesion adhering to the substrate. Through this process,
It becomes possible to minimize the deterioration of the solution containing at least a surfactant in the next tank. Next, the substrate is immersed in a solution containing at least a surfactant, but by first immersing the substrate, the surfactant enters the interface between the substrate and the dirt, thereby reducing the adhesion between the substrate and the dirt. Can be done. Furthermore, dirt is removed from the substrate by ultrasonic cleaning, but by keeping the available gas concentration above the concentration at which small bubbles appear in the liquid, the dirt is wrapped in air bubbles and is removed more quickly. Peels off from the substrate surface. Up to this point, most of the stains have been peeled off from the substrate, but if there are stains that are more strongly adhered, they are dissolved in the next organic solvent that freely mixes with water. Since organic solvents are expensive, it is necessary to remove as much dirt as possible in the previous steps. Due to these factors, cleaning time can be shortened and costs can be reduced.

[0015]

【Example】

(Examples 1 to 9) Next, cleaning methods according to Examples 1 to 9 of the present invention will be explained.

First, a plastic flat lens having a diameter of 65 mm and a thickness of 3.6 mm manufactured by polymerizing diethylene glycol bis(allyl carbonate) as a main raw material was used as a substrate to be cleaned.

[0017] Dirt is raw material monomers, oligomers, and polymers that adhere to the substrate during manufacture of the substrate.

The shower was performed with 20 liters of city water per minute. The surfactant in the immersion solution is non-ionic (Johnson
alkaline cleaner M-6000), the concentration is 10
%. The ultrasonic cleaning solution used the same surfactant as the immersion solution, and the concentration was 1%. Ultrasonic waves have a frequency of 28kHz,
Output 500W (Shimada Rika Kogyo MODEL)
ET50S-7) was used. The dissolved gas concentration in the cleaning liquid was measured using a dissolved oxygen meter (Horiba DO-8F) and a DO electrode (Horiba 5410), replacing the dissolved oxygen concentration. Table 1 shows the dissolved oxygen concentration and the type of organic solvent used.

[0019]

[Table 1]

[0020] Drying is done by drying the substrate for 3 m from pure water at a temperature of 60 degrees Celsius.
After being pulled up at m/Sec, it was dried with warm air.

[0021] Cleaning evaluation was performed using a surface foreign matter defect device (Hitachi Decor, HLD300B) using visual inspection and laser light scattering method.
The number of dust particles of 0.2 microns or more was measured using the following. The results are shown in Table 2.

[0022]

[Table 2]

As shown in Table 2, in the cleaning methods according to Examples 1 to 9, if the dissolved oxygen concentration is 7 ppm or more, the cleaning results are good regardless of the type of organic solvent. On the other hand, in Comparative Examples 1 to 6, sufficient cleanliness was not obtained.

Furthermore, as shown in Comparative Example 7, sufficient cleanliness was not obtained even when the cleaning step with an organic solvent was omitted.

(Examples 10 to 18) Next, Examples 10 to 18 were prepared by changing the surfactant from Examples 1 to 9.
The cleaning method related to this will be explained.

The cleaning methods of Examples 1 to 9 were changed only in the types of immersion liquid and ultrasonic cleaning liquid, and other conditions were the same as in Example 1. Table 3 shows the types of surfactants used in the immersion and ultrasonic solutions.

[0027]

[Table 3]

The drying and evaluation methods were also similar to Examples 1 to 9. The evaluation results are shown in Table 4.

[0029]

[Table 4]

As shown in Table 4, in the cleaning methods according to Examples 10 to 18, the cleaning results were good regardless of the type of surfactant.

(Examples 19 to 24) Next, cleaning methods according to Examples 19 to 24 in which the cleaning substrate and the type of dirt were changed will be described.

Six types of substrates and stains shown in Table 5 were cleaned using the cleaning method of Example 1.

[0033]

[Table 5]

The drying and evaluation methods were the same as in Examples 1 to 9. The evaluation results are shown in Table 6.

[0035]

[Table 6]

As shown in Table 6, in the cleaning methods according to Examples 19 to 24, the cleaning results were good regardless of the type of substrate and the type of dirt.

Next, the cleaning performance when the shower step/immersion step is omitted will be described.

(Examples 25 to 27) Example 2 for explaining Comparative Examples 7 to 9 when the shower step is omitted
The cleaning methods according to items 5 to 27 will be explained.

Although cleaning was performed using the cleaning method of Example 1, Examples 25 to 27 are the 10th, 20th, and 30th sheets that were cleaned using the same cleaning solution, respectively. Example 28 is the first sheet that was cleaned from Example 1 by omitting the shower step. Similarly, Comparative Examples 7 to 9 are the 10th, 20th, and 30th sheets that were washed from Example 1 without the shower step. Comparative Example 10 is obtained by omitting the dipping step from Example 1.

[0040] The drying and evaluation methods were similar to Examples 1 to 9. The evaluation results are shown in Table 7.

[0041]

[Table 7]

As shown in Table 7, in the cleaning methods according to Examples 25 to 27, if the shower step is performed,
Even in the second sheet, the number of foreign substances on the surface remains at a small level. Further, in the cleaning method according to Example 28, even if the shower step is omitted, the cleaning performance is not lost if it is the first sheet. On the other hand, in the cleaning methods according to Comparative Examples 7 to 9, if the shower step is omitted, satisfactory cleaning performance cannot be obtained even after the 10th sheet.

FIG. 1 shows the number of particles in the liquid measured in the rinsing tank after N-methyl-2-pyrrolidone in the cleaning methods of Example 1 (with shower step) and Example 28 (without shower step). Correlation with the number of sheets washed. The particles in the liquid were measured using a TD-30 particle counter manufactured by Sigma Tech, and expressed as the number of particles of 0.3 microns or more in 1 ml.

As shown in FIG. 1, the samples that were subjected to the shower process are clearly inferior to the samples that were not subjected to the shower process in terms of the number of particles in the liquid, as well as the values measured by the surface foreign particle defect device. From this, the presence of the shower step can prevent the cleaning liquid from deteriorating.

Furthermore, as shown in Comparative Example 10 in Table 7, the cleaning performance was clearly inferior even when the dipping step was omitted.

[0046]

Effects of the Invention As described above, the present invention prevents the deterioration of the cleaning solution from the next tank onwards and extends the life of the solution by removing weakly adhesive dirt in advance through shower cleaning. Next, cleaning time can be shortened by performing immersion in advance before applying ultrasonic waves and keeping the dissolved gas concentration in the cleaning liquid above a certain value. Next, the quality of the cleaned product can be improved by performing a final cleaning using an organic solvent that mixes freely with water. Furthermore, since both washing and drying can be carried out without using any solvents such as Freon 113, trichlene, triethane, or dichloromethane, the washing process can be carried out under environmentally advantageous conditions. This is an excellent cleaning method from the various points mentioned above.

[Brief explanation of drawings]

FIG. 1 is a diagram showing that the shower step in the present invention prevents deterioration of the cleaning liquid.

Claims (8)

[Claims] 1. In cleaning a substrate to which at least one of monomers, oligomers, or polymers has adhered, there is a step of shower cleaning using at least an aqueous solution, a step of immersing the substrate in a solution containing at least a surfactant, and then a step of immersing the substrate in a solution containing at least a surfactant; A step of performing ultrasonic cleaning using an aqueous solution containing an activator and maintaining the dissolved gas concentration above a certain value, followed by immersion and cleaning using a solution containing at least an organic solvent that freely mixes with water. A cleaning method comprising a step of performing ultrasonic cleaning or immersion/jet cleaning, and further a step of drying by centrifugation, hot air, or pulling up pure water. 2. The cleaning method according to claim 1, wherein the substrate is a polymer. 3. The cleaning method according to claim 1, wherein the substrate is a polymer mold. 4. The cleaning method according to claim 1, wherein the dissolved gas is air and the dissolved oxygen concentration at room temperature is 7 ppm or more. 5. The cleaning method according to claim 1, wherein the substrate is a polymer, the dissolved gas is air, and the dissolved oxygen concentration at room temperature is 7 ppm or more. [Claim 6] The substrate is a polymer molding mold, the dissolved gas is air, and the dissolved oxygen concentration at room temperature is 7 ppm.
The cleaning method according to claim 1, wherein the cleaning method is as follows. 7. The cleaning method according to claim 1, wherein the organic solvent is N-methyl-2-pyrrolidone. 8. Claims 1 to 6, wherein the organic solvent is at least one selected from lower alcohols, ketones, cellosolves, and glycols.
Cleaning method as described.